Spatial variations in age-0+ Merluccius hubbsi (Patagonian stock; 45º-47ºS) feeding conditions through fatty acids composition

Abstract

Fatty acids (FA) play critical roles in trophic interactions in aquatic food webs, transferring from phytoplankton to fish, and being modulated by oceanographic conditions and productivity. FA are a well-established approach for studying fish feeding preferences, and can indicate habitat quality and ecosystem condition. Thus, they provide valuable information in the context of fisheries management. The aim of this research was to determine the FA profiles of age-0 + hake Merluccius hubbsi and their zooplankton prey (Euphausia spp., Munida gregaria, Themisto gaudichaudii), identify FA trophic markers, infer their diet in comparison with stomachs information, and evaluate spatial changes in FA indicators with respect to the austral spring environmental variability in the Patagonian nursery ground (San Jorge Gulf, SJG; 45º-47ºS, 65º30’−67º30’W). We hypothesize that age-0 + hake and zooplankton FA composition relate to frontal structures and chlorophyll-a concentration, revealing diatoms predominance in the SJG spring food web. Major FA in hake and zooplankton were 16:0, 16:1n7, 18:1n9, 20:5n3 and 22:6n3. Age-0 + hake profiles mostly resembled euphausiids FA composition, in agreement with the stomachs analysis. Bacterial (15:0 + 17:0 + 17:1 + 18:1n7) and a mixed signal from both diatoms (16:1n7 + 20:5n3) and dinoflagellates (18:4n3 + 22:6n3) were recorded in the profiles; these suggest the existence of a classical food web in central coastal waters of the gulf and an omnivorous one towards the north and south extremes. Results are useful for a better understanding of the SJG food web and the key role age-0 + hake play in energy transfer, contributing to ongoing M. hubbsi recruitment studies in the region.